1. Field of the Invention
The present invention relates to an image device comprising a panel having a pixel section, and more particularly to an image device comprising integrated circuits for supplying driving signals to the pixel section and an external connection board for supplying control signals to the integrated circuits.
2. Description of the Related Art
Image devices suitable for compact and thin construction have been strongly demanded for display devices used in portable personal computers, information apparatuses such as portable TVs, and terminal apparatuses such as portable telephones, or for printing devices such as those used in printers using liquid crystal shutters or in photographic printers (for example, photo printers) or the like. Liquid crystal displays, liquid crystal printers, etc. that use liquid crystals can meet such market needs.
Under these circumstances, liquid crystal devices are commonly used as image devices. In recent years, there has developed a need to increase the image resolution of such liquid crystal devices so that more image information can be handled while retaining the compact size of the device. That is, there has arisen a need to increase the number of wiring lines in the liquid crystal panel constituting the liquid crystal device, while making the entire construction of the liquid crystal device, including its drive circuitry, thin and compact in size. Responding to such needs, many inventions have been proposed, which include, for example, an image device equipped with drive circuits or control circuits mounted using a COG (chip-on-glass) technique which mounts driver ICs directly on the substrate of the liquid crystal panel constituting the liquid crystal device, and an image device in which a flexible or rigid board with drive circuits or control circuits mounted thereon is connected to the liquid crystal panel constituting the liquid crystal device.
Of the prior art image devices, the image device equipped with drive circuits mounted using the COG (chip-on-glass) technique which mounts driver ICs directly on the substrate of the liquid crystal panel constituting the liquid crystal device will be described below, as an example, by referring to an invention previously proposed by the Applicant and disclosed in Japanese Patent Application No. 2000-176257.
FIG. 11 is a diagram showing the structure of an essential portion of a liquid crystal display device, as prior art 1, in which driver ICs are mounted using the COG technique described above. FIG. 11(A) is a front view, and FIG. 11(B) is a top plan view. In FIGS. 11(A) and 11(B), reference numeral 201 is a top glass substrate, 202 is a bottom glass substrate, 203 is a segment electrode driver IC, and 204 is a common electrode driver IC. Further, reference numerals 205 and 205B indicate segment electrodes and segment electrode leads, respectively, formed on the lower surface of the top glass substrate 201. Reference numerals 206 and 206B indicate common electrodes and common electrode leads, respectively, formed on the upper surface of the bottom glass substrate 202. The top glass substrate 201 and the bottom glass substrate 202 are overlaid one on top of the other and bonded together via a sealing member 207 made of an insulating adhesive material, leaving their extended portions 201B and 202B extending in the vertical and horizontal directions, respectively, as shown in the figure. A liquid crystal cell is thus constructed.
The sealing member (sealing material) 207 is formed in such a manner as to encircle the periphery of the overlaid area, leaving an injection port opened (not shown) and thus forming a sealed space for a liquid crystal. The top glass 201 and the bottom glass 202 hold therebetween the liquid crystal (not shown) injected into the sealed space, and thus form a display area 208. In the display area 208, the plurality of segment electrodes 205 formed on the lower surface of the top glass substrate 201 and the plurality of common electrodes 206 formed on the upper surface of the bottom glass substrate 202 are arranged intersecting each other, forming a matrix array of a plurality of pixels 209 and thus forming a pixel section. (By applying a prescribed voltage between the segment electrode 209 205 and common electrode 206 corresponding to each target pixel by a known method, a desired character, graphic, etc. can be displayed).
The segment electrode leads 205B and input wiring lines 210 for the segment electrode driver IC are formed on the lower surface of the extended portion 201 B of the top glass substrate 201. The common electrode leads 206B and input wiring lines 211 for the common electrode driver IC are formed on the upper surface of the extended portion 202B of the upper glass substrate 202. An array of protruding connection terminals 203B not shown is provided on the bottom of the segment electrode driver IC 203, and the segment electrode driver IC 203 is mounted using the COG technique via an anisotropic conductive film not shown, with its connecting terminals 203B connected to the segment electrode leads 205B and the input wiring lines 210 for the segment electrode driver IC. Likewise, a similar connection terminal array 204B is provided on the bottom of the common electrode driver IC 204, and the common electrode driver IC 204 is also mounted in the same manner as described above, with its connecting terminals 204B connected to the common electrode leads 206B and the input wiring lines 211 for the common electrode driver IC.
The input wiring lines 210 for the segment electrode driver IC and the input wiring lines 211 for the common electrode driver IC are each connected to an external circuit via a flexible printed circuit (FPC) not shown.
In the above structure, when a segment electrode driving signal is applied from the external circuit to the segment electrode driver IC 203 via the FPC through the input wiring lines 210 for the segment electrode driver IC, the segment electrode driver IC 203 generates a segment electrode driving voltage, and the driving voltage is applied to each segment electrode 205 via the corresponding segment electrode lead 205B. Likewise, when a common electrode driving signal is applied from the external circuit to the common electrode driver IC 204 via the corresponding FPC through the input wiring lines 211 for the common electrode driver IC, the common electrode driver IC 204 generates a common electrode driving voltage, and the driving voltage is applied to each common electrode 206 via the corresponding common electrode lead 206B. As a result, a prescribed voltage corresponding to the driving signals is applied to the liquid crystal at each pixel 209 in the display area 208, producing the desired display by controlling the light transmittance of the liquid crystal.
In this way, the liquid crystal display device shown in FIG. 11 is thin in construction and is capable of producing the necessary display. However, in this liquid crystal display device, the extended portions 201B and 202B extending in the vertical and horizontal directions from the display area must be provided in order to mount the driver ICs thereon. As a result, the liquid crystal panel, when viewed from the top, is not rectangular in shape, but has a complex top plan shape that is asymmetric between left and right.
Generally, for a liquid crystal display device, a housing having a simple top plan shape such as a rectangular shape is used for the convenience of use and for aesthetic appearance; as a result, the above prior art liquid crystal display device has the problem that the object of reducing the size cannot be achieved because the top plan dimensions of the construction, including the housing, become substantially large compared with the display area 208.
It is known to provide a liquid crystal display device of the structure shown in FIG. 12 as prior art 2 that resolves the problem associated with the asymmetric shape shown in FIG. 11. In FIG. 12, reference numeral 221 is the top glass substrate, and 222 is the bottom glass substrate. The top glass substrate 221 and the bottom glass substrate 222 have the same horizontal width, and substantially the same vertical length. The top glass substrate 221 and the bottom glass substrate 222 are not displaced horizontally, but displaced vertically relative to each other in opposite directions, and are bonded together via the sealing member 207, leaving their extended portions 221B and 222B exposed as shown in the figure. On the lower surface of the top glass substrate 221 are formed the segment electrodes 205, the segment electrode leads 205B which are extensions of the segment electrodes, and the input wiring lines 210 provided independently of the segment electrode leads.
Here, the input wiring lines 210 are formed near the vertical edge of the extended portion 221B of the top glass substrate, and the segment electrode leads 205B are formed extending from the extended portion 221B to the sealed area 228 enclosed by the sealing member 207, while the segment electrodes 205 are formed within the sealed area 228.
Indicated at 206C are common electrode routing lines connecting between the common electrodes 206 and the common electrode leads 206B in integral fashion. The common electrodes 206, the common electrode routing lines 206C, the common electrode leads 205B, and the input wiring lines 211 provided independently of the common electrode leads are formed on the upper surface of the bottom glass substrate 221.
Here, the input wiring lines 211 are formed near the vertical edge of the extended portion 222B of the bottom glass substrate, and the common electrode leads 206B are formed extending from the extended portion 222B to the sealed area 228 enclosed by the sealing member 207, while the common electrodes 206 and the common electrode routing lines 206C are formed within the sealed area 228.
In the sealed area 228, the common electrodes 206 and the segment electrodes 205 are arranged intersecting each other, forming a matrix array of pixels 209 from their intersections. The common electrode routing lines 206C are formed in routing areas 230A and 230B in the sealed area 228 on the left and right sides of the display area 228 comprising the pixels 209. When the number of common electrodes 206 is 4n, for example, the number of common electrode routing lines in each of the left and right routing areas 230A and 230B is 2n. In a manner similar to that already described, the input wiring lines 210 and the segment electrode leads 205B are connected to the segment electrode driver IC 203, and the input wiring lines 211 and the common electrode leads 206B are connected to the common electrode driver IC 204.
In the above structure, when prescribed driving signals are applied from the outside to the segment electrode driver IC 203 and the common electrode driver IC 204 through the respective input wiring lines 210 and 211 in a manner similar to that previously described, the light transmittance of each pixel 209 in the display area 229 is controlled based on substantially the same principle as previously described, and the desired display is produced. As shown in FIG. 12, in the prior art 2, the liquid crystal panel is symmetrical between left and right, and the space efficiency of the housing is better than that of the liquid crystal panel shown in FIG. 11.
In the prior art 2, since the top plan shape of the liquid crystal panel comprising the top glass substrate 221 and bottom glass substrate 222 bonded together via the sealing member 207 is substantially rectangular, the liquid crystal panel can be accommodated efficiently utilizing the space within a housing whose top plan shape is rectangular; however, since the width is extended left and right as shown in FIG. 12, the prior art 2 has not been effective in achieving a sufficient size reduction. This has been particularly true in the case of portable telephones that have recently become ubiquitous in the market.
In view of this, a method has been devised that integrates the common electrode driving circuit and the segment driving circuit into a single integrated circuit. With this method, the segment driver IC 203 and the common electrode driver IC in FIG. 12 can be combined into one IC. In fact, products using such an IC have been around in recent years.
It will, however, be noted that while each common electrode is selected and driven once in each frame or field period, in the same field or frame period each segment electrode is supplied with substantially as many pulses as there are segment electrodes. For example, in the case of a liquid crystal panel having 128 segment electrodes, up to the 128 segment electrodes are selected during one common electrode selection period.
In this way, the number of pulses that the segment driving circuit applies to each segment electrode is larger than the number of pulses that the common electrode driving circuit applies to each common electrode, and as a result, if the operating voltage of the segment driving circuit is increased, current consumption increases, increasing the power consumption and hence the switching noise; therefore, usually use is made of a means that reduces the operating voltage of the segment driving circuit and relatively increases the operating voltage of the common electrodes.
One possible method is to integrate the common electrode driving circuit and segment driving circuit with different supply voltages or driving circuits with different operating voltages into a single integrated circuit or IC, but in that case, the fabrication of the integrated circuit becomes difficult because of noise, power consumption, and the complexity of the fabrication process, leading to the problem of increased IC cost. Furthermore, since the number of input terminals and output terminals on the integrated circuit increases, it is difficult to arrange the terminals within the limited surface area of the integrated circuit, and besides, highly precise positioning of the integrated circuit becomes necessary, resulting in the problem of increased production cost. Further, if the integrated circuit is rendered defective during the production process, etc., the expensive integrated circuit has to be discarded as a matter of course, leading to the problem that the cost associated with such losses increases.
Besides the above method using the COG, the method disclosed in Japanese Unexamined Publication No. 63-184781 and described below as prior art 3 has also been used as a method for supplying driving signals to the liquid crystal panel. In this method, electrode driver ICs are mounted on FPCs each of which is connected at one end to the liquid crystal panel by an anisotropic conductive adhesive material or the like.
The prior art 3 related to the present invention will be described with reference to FIG. 13 taken from Japanese Unexamined Publication No. 63-184781. In FIG. 13, the liquid crystal device 230 comprises a glass substrate on which common electrodes are formed, a glass substrate on which a plurality of segment electrodes are formed, and a liquid crystal sandwiched between the two glass substrates, thus forming a liquid crystal display area 215. Lead electrodes for the common electrodes and segment electrodes are formed on the four sides of one glass substrate. Circuit boards 232 constructed from FPCs with X-driver IC chips 216, Y-driver IC chips 217, and a control IC chip 218 mounted thereon are provided on the four sides of the glass substrate, and the lead electrodes on each circuit board 232 are connected at a connection part 219 to the corresponding lead electrodes on the liquid crystal panel 231 by using an anisotropic conductive adhesive material.
To connect the lead electrodes by an anisotropic conductive adhesive material, the anisotropic conductive adhesive material, which is prepared by mixing conductive particles and nonconductive particles in a thermoplastic resin binder, is applied between the electrodes which are then connected and bonded together under heat and pressure.
Since the electrode driver ICs are mounted on the FPCs, the prior art 3 has advantages over other prior art in that a defective electrode driver IC is easily replaceable, and in that there is no need to provided within the liquid crystal panel the electrode driver IC mounting space for mounting the driver ICs using the COG technique. However, in the liquid crystal device of the prior art 3, to connect the outputs of the driver ICs to the liquid crystal panel, extended portions are provided in the vertical and horizontal directions of the display area and connected at at least two places to the FPCs, one for common electrode driving and the other for segment electrode driving. The resulting problem is that the top plan size of the liquid crystal device becomes large.
Generally, for a liquid crystal display device, a housing having a simple top plan shape such as a rectangular shape is used for the convenience of use and for aesthetic appearance; as a result, the above prior art liquid crystal display device has the problem that the object of reducing the size cannot be achieved because the top plan dimensions of the construction, including the housing, become substantially large compared with the display (pixel) area 215.
The arrangement of wiring lines on an FPC that are connected to the input or output terminals of an electrode driver IC when mounting the electrode driver IC on the FPC in the prior art 3 will be described below as prior art 4 with reference to Japanese Unexamined Patent Publication No. 2-69720.
FIG. 14 shows a wiring pattern on the substrate side of an electrode driver IC mounting area in a color liquid crystal panel, in which reference numeral 241 indicates the wiring lines on the input side and 242 the wiring lines on the output side. An input signal is input through the input wiring lines 241 into the electrode driver IC mounted on the electrode driver IC mounting area 243, the area enclosed by dashed lines in the figure, and the signal is processed by the electrode driver IC and output as a driving signal through the output wiring lines 242. The thus output driving signal is used to drive the liquid crystal. Substantially the same wiring pattern is used for the substrate side wiring pattern in COG mounting.